Mixed martial arts (MMA) is a full contact combat sport that allows a wide variety of fighting techniques, from a mixture of martial arts traditions and non-traditions, to be used in competitions. The rules allow the use of striking and grappling techniques, both while standing and on the ground. Such competitions allow martial artists of different backgrounds to compete.

The idea is to combine techniques from various combat systems each within a different combat range, and thus to be effective in all of them, just as in MMA. The forerunner of this idea was Bruce Lee and his brainchild Jeet Kune Do, which is by many considered the forerunner of MMA.

Modern mixed martial arts competition emerged in American popular culture in 1993 with the founding of the Ultimate Fighting Championship. Initially based on finding the most effective martial arts for real unarmed combat situations, competitors of various arts were pitted against one another with minimal rules for safety. In the following decade, MMA promoters adopted many additional rules aimed at increasing safety for competitors.

The early years of the sport saw a wide variety of traditional styles - everything from sumo to kickboxing - but the continual evolution of the sport saw many styles prove ineffective, while others proved successful on their own.

In the early 1990s, three styles stood out for their effectiveness in competition: Brazilian Jiu-Jitsu, amateur wrestling and shoot wrestling.

As competitions became more and more common, those with a base in striking became more competitive as they acquainted themselves with takedowns and submission holds, leading to notable upsets against the then dominant grapplers. Subsequently, those from the varying grappling styles added striking techniques to their arsenal. This overall development of increased cross-training resulted in the fighters becoming increasingly multi-dimensional and well-rounded in their skills.

Today, mixed martial artists must cross-train in a variety of styles to counter their opponent's strengths and remain effective in all the phases of combat. Popular displines include:

- Stand-up: Various forms of boxing, kickboxing, Muay Thai and forms of full contact karate are trained to improve footwork, elbowing, kicking, kneeing and punching.
- Clinch: Freestyle, Greco-Roman wrestling, Sambo and Judo are trained to improve clinching, takedowns and throws, while Muay Thai is trained to improve the striking aspect of the clinch.
- Ground: Brazilian Jiu-Jitsu, shooto, catch wrestling, Judo and Sambo are trained to improve ground control and position, as well as to achieve submission holds, and defend against them.

The rules for modern mixed martial arts competitions have changed significantly since the early days of vale tudo, Japanese shoot wrestling, and UFC 1, and even more from the historic style of pankration. As the knowledge about fighting techniques spread among fighters and spectators, it became clear that the original minimalist rule systems needed to be amended. The main motivations for these rule changes were protection of the health of the fighters, the desire to shed the image of "barbaric, no rules, fighting-to-the-death" matches, and being recognised as a sport.

The new rules included the introduction of weight classes; as knowledge about submissions spread, differences in weight had become a significant factor.

Small, open-fingered, gloves were introduced to protect fists in punches, reduce the occurrence of cuts (and stoppages due to cuts) and encourage fighters to use their hands for striking to allow more captivating matches. Time limits were established to avoid long fights with little action where competitors conserved their strength. Matches without time limits also complicated the airing of live events. Similar motivations produced the "stand up" rule, where the referee can stand fighters up if it is perceived that both are resting on the ground or not advancing toward a dominant position.

Victory in a match is normally gained either by the judges' decision after an allotted amount of time has elapsed, a stoppage by the referee (for example if a competitor can not defend himself intelligently) or the fight doctor (due to an injury), a submission, by a competitor's cornerman throwing in the towel, or by knockout.

The techniques utilized in mixed martial arts competition generally fall into two categories: striking techniques (such as kicks, knees and punches) and grappling techniques (such as clinch holds, pinning holds, submission holds, sweeps, takedowns and throws). The first ever and largest MMA Sanctioning body in the world today is the International Sport Combat Federation (ISCF). Although sanctioning bodies such as the ISCF have rules and regulations for MMA, rules may vary between promotions. While the legality of some techniques (such as elbow strikes, headbutts and spinal locks) may vary, there is a near universal ban on techniques such as biting, strikes to the groin, eye-gouging, fish-hooking and small joint manipulation.

Mixed martial arts promotions typically require that male fighters wear shorts as the only permissible attire, thus precluding the use of gis or fighting kimonos to inhibit submission holds.

The need for flexibility in the legs combined with durability prompted the creation of various fighting shorts brands, which then spawned a range of mixed martial arts clothing and casualwear available to the public.

Nothe that the term MMA may also be used, less correctly, to describe all kinds of hybrid martial arts styles in general.